When people ask if a material is magnetic, they usually want a simple yes or no answer about whether it will stick to a magnet. Magnetism, however, is a continuous spectrum of physical responses to an applied magnetic field, not a binary concept. Therefore, the answer for magnesium requires a detailed explanation of how it responds at the atomic level. Understanding magnesium’s behavior requires looking into the specific magnetic classifications that govern all matter.
The Definitive Answer: Magnesium’s Magnetic Classification
Magnesium is not magnetic in the way most people understand the term. It is definitively not ferromagnetic, meaning it will not be attracted to a standard magnet nor can it be permanently magnetized. Ferromagnetism is the strong attraction exhibited by materials like iron, nickel, and cobalt. Magnesium belongs to a much weaker category of magnetic materials.
Metallic magnesium is classified as paramagnetic, representing a very weak attraction to an external magnetic field. This slight attraction is only present while the material is actively placed within that field. Once the external magnet is removed, magnesium loses all induced magnetic properties and returns to its non-magnetic state. This behavior is millions of times weaker than the attraction seen in ferromagnetic substances.
The weak nature of paramagnetism means that for all practical purposes, magnesium is considered a non-magnetic metal. Measuring this subtle interaction requires extremely sensitive laboratory equipment, such as a SQUID magnetometer. The magnetic force exerted on magnesium is far too small to overcome gravity or friction, which is why a magnet cannot pick up a piece of the metal.
Understanding Paramagnetism at the Atomic Level
The magnetic behavior of any material stems from the movement of electrons within its atoms. It depends on whether the electrons exist in a paired or unpaired state within the atomic orbitals. Paramagnetism typically arises in atoms that possess one or more unpaired electrons, each acting like a tiny, randomly oriented magnet called a magnetic moment.
When an external magnetic field is applied, these individual moments briefly align themselves parallel to the field, creating a net attraction. This attraction is weak because the thermal energy of the atoms constantly works to randomize the alignment. Magnesium’s atomic structure, with its paired electrons, might suggest a different behavior, but the metallic form is a special case.
In solid metallic magnesium, the valence electrons become delocalized, forming a “sea” of conduction electrons free to move throughout the structure. These free electrons contribute to a phenomenon known as Pauli paramagnetism. When exposed to an external field, the energy states of these conduction electrons shift slightly, resulting in the subtle, weak attraction that defines magnesium’s paramagnetic classification. This effect is often balanced against a weak repulsion from other electron interactions, which is why metallic magnesium is near the border between paramagnetism and diamagnetism.
Comparing Magnetic Behaviors: Magnesium vs. Common Metals
Magnesium’s paramagnetic classification puts its magnetic response in stark contrast to the materials most people encounter daily. Ferromagnetic materials, such as iron, possess a massive, positive magnetic susceptibility, meaning they become strongly magnetized in a field and retain that magnetism due to the cooperative alignment of neighboring atomic moments within structures called domains. This cooperative alignment of these domains is what makes the attraction so powerful.
Magnesium, by comparison, has a very small, positive magnetic susceptibility, typically measured around 1.2 x 10^-5 (dimensionless volume susceptibility). This value is minuscule compared to the susceptibility values of ferromagnets, which can be thousands or tens of thousands of times larger. This vast difference highlights why magnesium is functionally non-magnetic.
Other common materials, like pure copper or water, are diamagnetic, meaning they exhibit a slight repulsion from a magnetic field. Diamagnetism occurs because all electrons are perfectly paired, inducing a temporary, opposing magnetic field when an external field is present. Magnesium’s weak attraction distinguishes it from this repulsive behavior. However, both effects are so faint they fall into the general category of materials considered non-magnetic outside of a laboratory setting.